1. Field of the Invention
The invention relates to glass coverings with temperature-controlled translucency, i.e., light transmission that responds to a given threshold temperature.
2. Description of the Related Art
In most parts of the world it happens at least during the summer months that temperatures in enclosed or roofed-over spaces that are inhabited or otherwise used exceed the comfort range and/or are incompatible with the uses for which the spaces are intended. In many cases, incoming light adds considerably to the warming effect. The usual transparent glass coverings made of mineral glass or plastics normally act as a block to heat penetration. The next most obvious means of relief, used since time immemorial, is to reduce or shut out incoming light when certain measurements call for it, in particular when room temperature requires it, by means, for example, of shutters, jalousies, blinds, curtains and the like. It entails placing light-reflecting and/or absorbing layers inside or preferably outside the spaces in question, and this process can even be automated--although at considerable cost.
Special regulating equipment with all its associated costs and risks could be dispensed with if one could succeed in using the incoming light and/or the resulting heat itself for purposes of regulating heat or the transmission of light.
Substances with reversible, temperature-dependent transparency are the subject matter of DE-OS No. 27 38 253. Such substances are composed of at least one optically transparent polymer and/or resin material as a matrix (A) and at least one organic substance (B) at least partially insoluble in said matrix material which when embedded in the matrix material melts or solidifies at the critical temperature to alter optical transparency and whose index of refraction either above or below the critical temperature for optical transparency change essentially coincides with the index of refraction of the matrix material. (B) constitutes at all times a discrete dispersed phase embedded in (A). As suitable organic substances (B), substances of low molecular weight are mentioned, such as alkanols, alkyl amines, alkanes, alkenes, alkynes, saturated or unsaturated mono- or di-carboxylic acids, their esters and amides, halogen fatty acids, aryl carboxylic acids and their derivatives, thioalcohols, thiocarboxylic acids and their derivatives, etc.
Said substances are intended for use in temperature measurement devices, heat devices or screening devices for greenhouses, cold frames, industrial structures, office, residential and car windows and the like.
DE-OS No. 29 07 352 discloses the use of similarly synthesized systems containing crystallites or droplets of low molecular weight substances (preferably M=300-500) in dispersed form embedded in a polymer matrix for purposes of data storage.
JP-OS No. 83 78 758 (Chem. Abstr. 99 213730n) describes a temperature sensitive light-screening material that is composed of laminates of transparent panes with layers containing poly-N-isopropylmethacrylamide, water and if necessary, an additive to regulate the cloud point. DE-OS No. 26 58 643 discloses a glass-gel-glass sandwich structure with variable transparency. An acrylamide-N-methylolacrylamide copolymer is recommended for the fluid that irreversibly changes to a gel state at room temperature; the variability of transparency is achieved by the addition of polymethyl vinyl ether or vinyl caprolactam.
U.S. Pat. No. 4,307,942 discloses a device for preventing the penetration of sunlight above a given temperature that consists of a layer of a porous polymer material, a solvent and a temperature-sensitive substance with which the porous material is impregnated and which has negative solution entropy at the indicated temperature range.
A thermoplastic film with temperature-dependent light transmission is described in JP-OS No. 76 132241 (Chem. Abstr. 86, 91221n).
Such a thermoplastic film with polymer particles dispersed in it with diameters of 1-150.mu. is supposed to allow at 40.degree. C. less than 90% of the transmission allowed at 10.degree. C.
An example of one embodiment is a mixture of 25 parts of polymethyl methacrylate (PMMA) and 75 parts of an ethylene vinyl acetate copolymer (72:28) that is agitated for 10 min. at 180.degree. C. and 80 rpm and pressed into a layer 1 mm thick containing PMMA particles 5.mu. in diameter.
JP-OS No. 79 12 518 (Chem. Abstr. 91, 124387e) shows how to make resins that are transparent only within a narrow temperature range. For that purpose, 2 to 50 parts of an ethylene vinyl acetate copolymer containing 10% to 35% vinyl acetate by weight are dissolved in 50 to 98 parts of methyl methacrylate (MMA) or in a monomer mixture consisting primarily of MMA and are polymerized by the radical method between glass plates.
A need continues to exist for new and improved glass systems with temperature-controlled light transmission that can supplement or replace traditional glass. Such glass must meet the normal mechanical and optical requirements, must--if possible--be simple to synthesize, must entail no added requirements and problems in terms of apparatus or technique, in other words, must be economical.
The glass system should preferably possess reversible temperature-controlled light-transmission capacity, and its functioning capability should be guaranteed for as long a period of time as possible. It will be an advantage if the threshold or critical temperature at which the transition from light transmission to reduced light transmission to no light transmission occurs can be set in advance, but it must also remain reproducible.
Glass pursuant to the invention is intended first and foremost as protective glass for rooms and other functional units, such as parts of buildings or vehicles, in the form of roofs, walls, windows and doors.
The term "glass" as used in this specification shall denote not so much the non-crystalline "glassy" state of ny polymeric material, but rather such matter that had been shaped to meet the demands normally associated with glass in the art of glazing, which in addition displays temperature-controlled light transmission, particularly in the visible range.